The present invention relates to a detection system particularly, but not exclusively, detecting proximity of a person relative to a vehicle for initiating communication between a security system of the vehicle and a transponder carried by the person.
A security system for a vehicle has been developed which, instead of requiring remote activation by a transceiver or transponder, can be activated by movement of a door handle of the vehicle. An activation or unlock signal is generated by the security system to disengage a mechanical latch mechanism of the door when the person grips and moves the door handle. A system of this type can also be used for entry to other restricted areas, such as domestic or commercial dwellings.
A disadvantage of the above security system is that an authorized person wishing to gain entry through the door may grip and move the door handle faster than the security system is able to unlock the door. Not only does this give rise to frustration to users of the system, but it can also result in persons sustaining physical injury if the door is not unlocked in time.
An alternative security system is described in German Patent Application No. DE 19620059, wherein a capacitive proximity switch is provided in a door handle. The switch includes a plurality of electrodes arranged for capacitive coupling therebetween, such that proximity of a person""s hand is detected without the need for separate movement of the door handle.
It is an object of the present invention to provide an improved detection system utilizing a capacitive proximity switch.
In accordance with the present invention, there is provided a detection system including a switch device having a conductor forming part of a capacitor having variable capacitance dependent upon proximity of a person, and a detector for sensing variation in the capacitance and for generating an output signal indicating the proximity of the person relative to the conductor, wherein the switch device further includes a retaining body adapted to mount the conductor to a door handle, the retaining body also having a switch arranged for actuation by a person gripping the handle to additionally or alternatively indicate the proximity of the person.
In another aspect, there is provided a switch device for use in the above-described detection system, the device including a conductor for forming part of a capacitor for detecting proximity of a person, a switch and a retaining body housing the conductor and switch and arranged to mount the device to a door handle.
Preferably, the body is a membrane with the conductor and switch embedded therein in juxtaposed relation.
Preferably, the switch is a mechanical switch formed of two or more conductive plates separated by electrically insulative material and adapted for relative displacement into electrical contact for actuation of the switch. More preferably, the conductor forms one of the plates of the mechanical switch. Alternatively, the switch includes a piezoelectric strip which produces a detection signal when the person grips the handle and imparts relative movement of a part of the strip.
Preferably, the detector includes an oscillator coupled to the conductor and a phase comparator, such that the variation in the capacitance results in an associated change in frequency of oscillation in the oscillator, to produce a phase modulated signal therein which is input to the phase comparator so as to generate a signal representative of this change in frequency.
Preferably, the phase comparator forms part of a phase-locked loop circuit and the detector further includes a comparator arranged whereby the feedback/error signal of the circuit is input to the comparator for comparison with a threshold level so as to generate the output signal indicating proximity of the person.
Alternatively, the phase-locked loop circuit and comparator may be replaced with a microcontroller which monitors the oscillator to determine quiescent frequency characteristic and generates an output signal indicative of the proximity of the person upon detecting variation, above a threshold level, of the frequency characteristics. The microcontroller may be programmed to adjust the threshold level in accordance with changes to the frequency characteristics introduced as a result of temperature variation.
In another aspect, there is provided a security system including a control unit, the above-described detection system and a lock, the control unit actuating an interrogation procedure, upon detection of proximity of the person, for checking security associated with the person and releasing the lock if the security requirements are met.
Preferably, the security system is a vehicle locking or disabling system which is actuated by the control unit for interrogation of a corresponding transponder carried by the person.